Almost everyone who exercises has felt the occasional “uh-oh moment,” when you feel a twinge in your knee, a pain in your foot, or an ache in your shoulder. According to More magazine, most twinges aren’t serious, and will heal on their own. Still, pain is your body’s way of sending you a message. So, here are the exercise aches you should never ignore:

• Symptom #1: Pain. A little discomfort during exercise is normal, especially if you’re trying to improve your fitness. However, if the pain lingers, is severe, or changes your behavior, see a doctor. For example, a pain that shoots down your leg could mean you injured a disc in your back, and need medical attention.
• You should also stop exercising immediately if you hear a pop. Severe injuries are often accompanied by an audible pop, including a tear in the ACL ligament in your knee.
• Another issue not to ignore: If there’s swelling, or you can’t put your weight on your foot. Swelling in a joint or soft tissue means your body’s responding to an injury. If your foot, ankle, knee, or hip feels weak or wobbly, it’s a sign you’ve done significant damage.So, see a doctor.
• You should also pay attention if you feel unusually tired. Chronic fatigue, muscles that tire easily, and painful tendons can be signs of a thyroid problem. So, talk to your doctor about getting your thyroid tested.
• Finally, stop exercising immediately if you feel headachy and nauseated. Those are two signs of hyponaetremia, a potentially fatal electrolyte imbalance caused by abnormally low blood sodium. It affects 13% of recreational marathon runners, and often occurs during long, intense bouts of exercise. When you sweat a lot and drink water to hydrate, it dilutes the sodium in your blood – and can cause severe brain swelling.